The subject matter of this invention broadly relates to reinforced plastics having impact resistance, uniformity of pigmentation, smooth surfaces (low profile) and good paintability. More specifically, it relates to unsaturated polyester or vinyl ester resin compositions containing certain polydiene rubbers and thermoset articles prepared therefrom.
Brittleness in reinforced plastics is a serious problem and a practical deterrant to their use in the manufacture of a variety of articles, such as car fenders, etc., where the highest possible impact resistance is essential. Currently, some manufacturer specifications for reverse impact properties make it difficult for most commercially available resins to be approved for such uses. In addition, other factors are of prime importance, (1) the resin should be capable of providing the smoothest possible surface to minimize the costs of surface preparation (sanding, etc.) for painting, (2) paint should adhere well to the molded article and (3) the resin should be capable of producing uniformly pigmented (non-mottled appearance) articles.
Attempts have been made to improve the surface properties (low profile characteristics) by incorporating into a resin such as an unsaturated polyester, a thermoplastic such as polymethyl methacrylate or polystyrene. Improvements in surface smoothness may be obtained, but paintability and/or impact strength are not improved. In addition, such resins pigment poorly and at best only light pastel colors have been possible. Attempts to prepare dark, molded colors have not been successful.
To overcome some of those problems, it was proposed in U.S. Pat. Nos. 3,674,893 and 3,857,812 to employ certain polydiene rubbers as an additive to vinyl ester resins and unsaturated polyesters. Those polydiene rubbers exhibited the desired beneficial results property wise. However, the solutions of resin and rubber were frequently so unstable as to phase separate in a short time. As a consequence, it was necessary to restrict the rubber additive to those of a stated range of viscosity and molecular weight. Also, it required the solutions to be either prepared immediately before use or to employ continuous stirring to maintain the single phase character of the solution. The improvement of the solution stability of such compositions would be of considerable benefit to their utilization in commerce.